1. Technical Field
Present embodiment relates to a fuel pressure control device.
2. Description of Related Art
In an internal combustion engine having a cylinder injection valve, a fuel pressurized with a low-pressure pump is further pressurized with a high-pressure pump, and the pressurized fuel is supplied to the cylinder injection valve through a high-pressure passage. In such an internal combustion engine, a fuel cut may be executed to temporarily stop fuel injection from the cylinder injection valve, for example. During the fuel cut, a high-pressure fuel in the high-pressure passage is not consumed, so that fuel pressure in the high-pressure passage may increase depending on the temperature of the fuel. As a result, the fuel pressure may become larger than a target fuel pressure when the internal combustion engine returns from the fuel cut. In this case, there is a possibility that a fuel injection amount in the cylinder injection valve, which receives fuel supply from the high-pressure passage, cannot appropriately be controlled.
Accordingly, for example in Japanese Patent Application Publication No. 10-54318 and Japanese Patent Application Publication No. 2010-71132, a technology for returning the fuel in the high-pressure passage to the fuel tank has been proposed in order to lower the fuel pressure in the high-pressure passage at the time of a pressure reduction request such as a fuel cut. Moreover, in Japanese Patent Application Publication No. 2000-18067, a technology has been proposed for continuing fuel injection until the fuel pressure in the high-pressure passage reaches a target fuel pressure when a fuel cut condition is satisfied.
However, the technology disclosed in JP 10-54318 A and JP 2010-71132 A requires a long relief passage for returning the fuel from the high-pressure passage to the fuel tank, which may cause increase in manufacturing costs. The technology disclosed in JP 2000-18067 A may cause a period of time from satisfaction of the fuel cut condition to execution of the fuel cut to be prolonged.
For example, in the technology of JP 2011-149407 A, a suction valve and a discharge valve are disposed on a low-pressure passage side and a high-pressure passage side of a compressing chamber of the high-pressure pump, respectively. The suction valve and the discharge valve can forcibly be opened by a single drive mechanism. In the technology disclosed in JP 2011-149407 A, both the suction valve and the discharge valve are opened by the drive mechanism so as to lower the fuel pressure in the high-pressure passage during the fuel cut.